Compound change gear transmissions of the type having one or more auxiliary sections connected in series with a main transmission section are very well known in the prior art. Such transmissions are typically associated with heavy duty vehicles such as large trucks, tractor semi-trailers, and the like. By utilizing main and auxiliary transmission sections connected in series, the total number of available transmission ratios is generally equal to the product of the main and auxiliary section ratios. For example, a compound change gear transmission comprising a four (4) speed main section connected in series with a three (3) speed auxiliary section will provide twelve (4.times.3=12) available ratios.
Auxiliary transmission sections may generally be characterized as range type, splitter type, or combined range and splitter type. In compound transmissions having a range type auxiliary section, the range section ratio step or steps are greater than the total ratio coverage of the main transmission section and the main section is shifted progressively through its ratios in each range. The assignee's well known RT/RTO Roadranger transmissions include a "(5).times.(2)" ten speed heavy duty range type transmission. In compound transmissions having a splitter type auxiliary section, the ratio steps of the splitter auxiliary section are less than the ratio steps of the main transmission section and each main section ratio is split, or subdivided, by the splitter section. In a combined range and splitter type auxiliary section, or sections, both range and splitter type ratios are provided allowing the main section to be progressively shifted through its ratios in at least two ranges and also allowing the main section ratios to be split in at least one range. Assignee's well known RT/RTO 11613 and RT/RTO 14718 "Eaton Roadranger" transmissions are examples of a "(4+1).times.(3)" thirteen-speed and a "(4+1).times.(4)" eighteen-speed combined range/splitter type transmission.
It should be noted that the terms main and auxiliary sections are relative and that if the designations of the main and auxiliary sections are reversed, the type of auxiliary section (either range or splitter) will also be reversed. In other words, given what is conventionally considered a four-speed main section with two-speed range type auxiliary section, if the normally designated auxiliary is considered the main section, the normally designated main section would be considered a four-speed splitter type auxiliary section. By generally accepted transmission industry convention, and as used in this description of the invention, the main transmission section of a compound transmission is that section which contains the largest (or at least no less) number of forward speed ratios, which allows selection of a neutral position, which contains the reverse ratio(s) and/or which is shifted (in manual or semiautomatic transmissions) by manipulation of a shift bar or shift rail or shift shaft/shift finger assembly as opposed to master/slave valve/cylinder arrangements or the like.
In compound transmissions of the range or the combined range/splitter or splitter/range types, the main transmission section is typically shifted using a shift bar housing assembly, or a single shift shaft assembly, controlled by a manually operated shift lever. The auxiliary range section is generally shifted using a button or a switch which controls a remote slave valve/actuator mechanism. In so-called "double H" or "one and one-half H" type controls, the range is shifted in response to switches which sense the position of the shift lever. The actuator mechanism typically includes a cylinder cover/valve assembly which directs pressurized fluid (air) to one side of the appropriate cylinder/piston while exhausting the opposite side. The pressurized fluid is supplied through a hose from a filter/regulator which reduces and regulates the fluid pressure while also filtering particulates. Prior actuator mechanisms employed a cast iron cylinder with a cast iron cylinder cover and a brass poppet valve inside the cover. This sometimes led to sticking of the valve resulting from galvanic corrosion of the spool and/or cylinder cover. Because the poppet valve travel was limited to reduce the time required to change states from open to closed, these valves were also vulnerable to sticking caused by contamination or particulates in the pressurized fluid.